Major Depressive Disorder (MDD) is one of the most common psychiatric illnesses, and is associated with substantial personal and societal costs. Difficulty removing negative information from working memory is a core cognitive feature of MDD. A growing body of research indicates that this cognitive difficulty is associated with the persistence of depressive symptoms and, in the face of negative events, with the tendency to repetitively ruminate about the negative aspects of such events. Rumination, in turn, is associated with impaired recovery from stress, both emotionally and biologically, which further contributes to symptom persistence. To date, research linking difficulty removing negative information from working memory with rumination, symptom persistence, and stress recovery has been limited by the use of correlational methodologies. Therefore, a major aim of the proposed study is to use established Cognitive Bias Modification methods to experimentally manipulate individuals' ability to remove negative information (RNI) from working memory. We propose to test the effects of RNI training on cognition, levels of rumination and depression, and emotional and biological recovery from stress. To achieve these aims, participants diagnosed with MDD will complete a laboratory- based pre-training session (Session 1), six at-home training sessions, and a second laboratory-based post- training session (Session 2). In Session 1, participants will complete a structured clinical interview, self-report measures of baseline rumination and depressive symptoms, and two computer-based cognitive tasks - one of which explicitly assesses their ability to remove negative information from working memory. Participants then will be randomly assigned to either Real RNI training or to a Sham RNI training condition. They will be taught how to perform the training tasks and will be provided with a laptop on which they will complete the training at home daily for the next six days. On the seventh day, participants will return to the laboratory for the post- training Session 2, during which they will complete the self-report measures and computer-based cognitive tasks that they completed in Session 1. In addition, participants will be exposed to a psychosocial stressor, during which we will measure stress-induced state rumination and assess psychological and biological recovery from the stressor. Compared to Sham RNI training, we expect that Real RNI training will a) increase participants' ability to remove negative information from working memory; b) decrease levels of depressive and ruminative symptoms from baseline; and c) decrease levels of stress-induced rumination, which we posit will, in turn, improve subsequent emotional and biological stress recovery. The results of this study will not only increase our understanding of the relations among cognition, rumination, and stress recovery, but will also provide insight into a novel and innovative treatment approach that has the potential to decrease rumination and improve psychological and biological responses to stress in MDD. Thus, we anticipate that the current study will contribute to both cognitive models of depression and clinical intervention efforts.